'We are between two fires so we choose the one that will burn us least'

It's a fitting symbol for a country that finds itself without the safeguards of a president or constitution – and now a parliament – nearly 18 months after a popular uprising drove Hosni Mubarak from power and ushered in a military junta supposedly committed to democracy.

And it's a political vacuum that Ayman says begins at his doorstep.

"We hear gunfire every day, drugs are being sold in broad daylight. People are too scared to stand on their balconies when the gangs arrive," Ayman laments, gesturing to the unpaved streets of this sprawling slum west of the Nile.

"There's no police, no security forces – it's like we're dead to them."

He expresses support for a secular strongman – Ahmed Shafik, a veteran of Mubarak's regime – as Egypt's next leader. But a moment later he is praising the "decent" Islamists whose candidate he backed in May's initial presidential election.

"Our revolution was a blessing from God," he says. "But if we elect one of Mubarak's men to replace him, how can we say we were successful?"

His son Eslam, 24, who is adding the finishing touches to a gold-painted wooden sarcophagus lined with hieroglyphs, has fewer qualms about turning back the clock to Mubarak's old guard.

"You see what's happening in Tunisia? The Salafists [hardline Islamists] are going crazy. The Brotherhood are no better. They came here with bread and cooking gas to win our votes. Once they got what they wanted, they abandoned us."

Such debates have echoed across Egypt's capital this weekend as a divisive presidential run-off goes ahead despite a legal ruling many believe marks a fully-fledged counter-revolution.

Today sees the second day of a poll pitting 71-year-old Shafik against Mohamed Mursi, a decade younger and the chairman of Egypt's erstwhile Islamist opposition, the Muslim Brotherhood.

They are polarising candidates: one a secular authoritarian with tacit military backing, the other a pious engineer pledging social and economic "renaissance" and a hazily defined version of Sharia law.

Both have core support that secured them roughly a quarter each of late May's first-round vote. But their politics – authoritarianism and Islamism – hold little appeal for those who backed secular or leftist contenders.

Shafik's tenure in Mubarak's corrupt regime, and his suggestion that executions be used to restore order, has prompted many to extend Mursi grudging support, despite misgivings over his movement's socially conservative plans.

Yet Thursday's ruling from Cairo's Constitutional Court – whose members were appointed by the ex-president – has revived long-held suspicions that Egypt's military rulers are rigging the game.

In a single stroke, a third of Egypt's recently elected members of parliament were ejected on a technicality, freezing the lower house and wresting its powers back under military control.

The move slashes the Islamist's majority – they won nearly 70% of seats in winter elections – and exposes them to a potentially damaging repeat vote. More crucially, it effectively wipes out the timetable for the transition to civilian rule.

Dissolved alongside parliament is the assembly charged with writing Egypt's new constitution, a document set to include the powers of the country's next head of state. Should Shafik be sworn in on July 1, it will be by a caretaker military parliament able to grant him carte blanche.

Two weeks after the verdict was returned on Mubarak – he was jailed for life for "failing to stop" violence against protesters, but six deputies walked free – activists believe the latest moves are a new attempt to roll back the uprising's fragile gains.

Last Tuesday, the justice ministry extended the military's power to arrest and investigate civilians, a partial return to the 30-year emergency law which was only cancelled in May. If Shafik wins, activists fear a revival of Mubarak's brutal security state.

"It's a military coup, plain and simple. We're preparing to take action," says Ahmed Maher, founding member of the April 6 Youth Movement, one of the groups that spearheaded last year's protests.

As yet little has happened on the street and the Brotherhood, the main loser in Thursday's ruling, has been restrained. Individual members cried counter-revolution, but Mursi and the group's political wing are battling on for the presidency.

"The Brotherhood still think they can win," said activist Marwa Nasser, 28, on Friday evening as a few hundred protesters reconverged on Tahrir Square, the focal point of 2011's uprising.

"They're not even among this crowd and they're one of the main reasons the revolution is losing. The Brotherhood fielded a presidential candidate after saying they wouldn't and that ended up splitting votes for the revolutionary candidates. This ruling on parliament is the last straw."

As the ballot opened yesterday, it was the culmination of three weeks of impassioned debate which has gripped Cairo like a fever. Shafik or Mursi? It's been the ubiquitous question in cafés, subway cars and taxis; the answer driving a wedge between neighbourhoods, city blocks and even within families for whom political discussion remains a novelty.

"At home we're divided," says Yasmine Rabie, 25, who lives in the middle-class reaches of Nasr City, eastern Cairo. "My father believes the state propaganda about the Brotherhood and the tales of their supposed militias; he thinks we need to vote Shafik to protect ourselves. Myself, my brother and mother are no fans of the Brotherhood but we'll choose Mursi."

It is this pragmatic "negative" vote that could work in the Brotherhood's favour. Even after Thursday's ruling, supporters of the Islamist contender seem, if not confident of victory, then certain that a Shafik presidency will face mass discontent.

Back in Giza, Mesbah Kosbr, a stout pensioner in a grey woollen galabeya, has covered his mobile phone store in Mursi bunting. He says: "We should really have a president from Tahrir Square but Mursi is the better choice. Shafik might win, only God knows. But the square can topple anyone."

Similar sentiments prevailed in Imbaba, a district that briefly fell under the control of militant Islamists in the early 1990s. Here motorised tuk-tuks swarm the streets, herds of goats feast on refuse piles and half-finished cinderblock tenements totter into the sky.

Despite its hardline reputation, Imbaba's voters tilted to popular socialist Hamdeen Sabbahi in the first round. But Brotherhood campaigners said the rebellious enclave will be instinctively against Shafik.

"We say to people, if you are worried about the Brotherhood then talk to us," insisted one female representative, shrouded in a pale blue chador. "The hijab, that's the most common concern. But we believe you can dress how you want – it is only God who will judge you, not Mursi."

Shafik's supporters are equally as invested in his victory. Mubarak's last prime minister is running on a simple, populist pledge to restore law and order, his campaign recasting his controversial military ties and political experience as strengths rather than moral failings.

His promises resound with Egypt's economic elites fearful of a recent crimewave, as well as some liberal Muslims and Christians unconvinced by the Brotherhood's apparently new-found tolerance.

On the main streets of Heliopolis, an upper-middle-class district of stucco villas and European-styled boulevards a brisk walk from Cairo's vacant presidential palace, there is a sense of besiegement.

Sitting behind the polished desk of his diamond brokerage, Sharif Ahmed points to empty display windows and the thick door of a heavy vault. "We don't put anything on show any more. We've had weeks with no business, the last thing we need is a theft," he says. Foreigners used to make up a third of his trade, he says, but the last year's plunge in tourism has slashed his profits – only an Islamic presidency that shatters the trade entirely could make things worse.

In a nearby boutique, its racks lined with low-cut dresses and swimsuits, the owner spoke of darker fears.

"I expect Shafik to collect the garbage – the terrorists," spits Sameh, 38, closing an empty fist beneath his chin to represent a bristling beard. "If they end up ruling they'll turn us back to the middle ages; it'll be like Kabul."

He nods across the street at a shopfront of mannequins in hijabs and more modest robes. "I'll have to become like them to survive," he jokes, his smile settling into a grimace. "Shafik has the keys, he has the army. He can take care of things."

Iman, in her late 30s, paying for summerwear, mutters what passes for dissent on these monied streets. "I can't vote for either, this isn't my country any more," she says, adjusting her scarf. "A killer or a fundamentalist? No thank you."

Egypt's Christians, who make up a sizeable presence in Heliopolis, could swing the election. Up to three million voted in the first round, mainly for Shafik and Sabbahi, and at least half that number are expected to head to the polls this weekend.

"We are between two fires so we choose the one that will burn us least," says Father Rafiq Greiche at the district's Greek Catholic Church. "People here supported the revolution but that changed when security didn't return and the Islamists usurped the political scene."

Now, he says, local residents with relatives in the United States and Canada are ready to emigrate at a few weeks' notice at the first signs of social restrictions.

Greater determination was found in the middle-class enclave of Zamalek, the central Cairo island of bistros and bars where Mursi gained less than 1% of May's vote.

In a Nileside tent, Alaa Al-Aswani, one of Egypt's best-known novelists, told a packed audience that a mass boycott was the only way to avoid giving legitimacy to an election engineered by the ruling military to bring Shafik to power.

"It's a mistake to consider this a real contest," he roared to bursts of applause.

"Shafik is coming – that's for certain. But the revolution continues."